Thank you Ian for the effort!
Although my LG sprocket looks very orginal it obviously is not right. Because it was pretty worn I already ordered a 42T one from Ken Lack. Hope it arrives soon.
I also tried to measure the HG sprocket. This is rather difficult as the beaks of my venier caliper are to wide to fit in the space between the sprocket and the drum. When trying to calculate it this one also results in 5 mm width. And also looks original (or at least old) and in very good condition. The chain that is on my bike now fits this sprocket perfectly which also indicates a 5 mm width.
But 5 mm width does not appear in any chaintables… I have send sprocketsunlimited an email to see if they can help.
So I guess I will have to get me a piece of 1/2×3/16 chain and see if this fits on the flywheel sprockets. If so, those would be original. If not, those would also be 5 width. At least I can do this without taking the flywheel out.
When the flywheel sprockets also are of 5 mm thickness I guess it would be wisest to make or get a new 5 mm wide LG sprocket and use the chainsize that is on my bike now. If the flywheel sprockets are the original 4,6 mm width I might want to change the HG sprocket and fit 1/2×3/16 chains all around.
Or are there any other options I am missing?